Among image forming apparatuses provided with developing cartridges, there is known an image forming apparatus capable of determining whether a developing cartridge is attached to the apparatus or capable of identifying specifications of the developing cartridge. For example, prior art discloses a developing cartridge that includes a detection gear, and protrusions that move as the detection gear rotates. The developing cartridge is attached to an image forming apparatus that includes a sensor for detecting the protrusions in a case where the developing cartridge is attached.